Double-click the Paintbrush tool to set the following options:

Fidelity

Controls how far you have to move your mouse or stylus before Illustrator adds a new anchor point to the path. For example, a Fidelity value of 2.5 means that tool movements of less than 2.5 pixels aren’t registered. Fidelity can range from 0.5 to 20 pixels; the higher the value, the smoother and less complex the path.

Smoothness

Controls the amount of smoothing that Illustrator applies when you use the tool. Smoothness can range from 0% to 100%; the higher the percentage, the smoother the path.

Fill New Brush Strokes

Applies a fill to the path. This option is most useful when drawing closed paths.

Keep Selected

Determines whether or not Illustrator keeps the path selected after you draw it.

Edit Selected Paths

Determines whether or not you can change an existing path with the Paintbrush tool.

Within: _ pixels

Determines how close your mouse or stylus must be to an existing path to edit the path with the Paintbrush tool. This option is only available when the Edit Selected Paths option is selected.